Process for finish-abrading optical-fiber-connector end-surface

ABSTRACT

To provide a process for finish-abrading an optical-fiber-connector end-surface without generating abrasion scratch on an abraded surface of optical fiber, nor generating an adherent substance. A process for finish-abrading an optical-fiber-connector end-surface which comprises a step of abrading an optical-fiber-connector end-surface with using an abrasive film ( 100 ) composed of abrasive grains ( 103 ) fixed on a film-form substrate ( 101 ), in the presence of a lubricating liquid, wherein the lubricating liquid is an aqueous solution containing a hydrophilic surfactant.

BACKGROUND

The present invention relates to a process for finish-abrading anend-surface of optical fiber equipped with a ferrule, that is, anoptical-fiber-connector end-surface.

Conventionally, an optical-fiber-connector which can be easily removedis widely used for connection of optical fibers in optical fibercommunication network. In the connection at the optical-fiber-connector,end-surfaces of the optical-fiber-connector made of optical fiber and acovering portion (ferrule) for covering the optical fiber, are allowedto directly abut each other. Therefore, the optical characteristics atthe time of connection, particularly connection loss, depend on theprocessing properties and precision of an optical-fiber-connectorend-surface.

An optical-fiber-connector end-surface is processed through severalabrasion steps. Usually, the steps of removing adhesives, abrading tocurved surface, secondary-abrading, and finish-abrading are conducted.The finish-abrading means abrasion at the final stage conducted withusing abrasive grains of the smallest size (a grain size of 5 to 1000nm), thereby surface roughness Ra of not more than 5 nm is provided.

Quality of the optical-fiber-connector end-surface is influenced byprocessing properties and precision in the final finishing abrasionstep. In other words, major factors for connection loss of the opticalfiber are degree of finishing roughness of the end-surface and itsinclination.

In the step of finish-abrading an optical-fiber-connector end-surface,superfine silica and the like was used as free abrasive grains in thepast. However the process using free abrasive grains is complicated inwork, so an abrasive film composed of abrasive grains fixed on afilm-form substrate, is widely employed at present.

The abrasive grains are fixed by a binder, and an abrasive layer, whichhas abrasive grains and a binder, is usually formed on a film-formsubstrate. Finish-abrading of an optical-fiber-connector end-surface isconducted by applying the optical-fiber-connector end-surface to anabrasive surface of the abrasive film and rubbing with a predeterminedamount of pressure.

Japanese Patent Laid-open Publication No. 248771/1997 discloses anabrasive tape for an optical-fiber-connector end-surface that has anabrasive layer containing abrasive grains and a binder on a substrate,the abrasive grains being silica particles having an average particlesize of 5 to 30 nm. Japanese Patent Laid-open Publication No. 71572/1998discloses an abrasive tape for optical fiber that has a primer layer andan abrasive layer containing abrasive grains and a binder on asubstrate, the abrasive grains being alumina-silica composite particleshaving an average particle size of 10 to 700 nm.

However, when abrasive grains of fine size are employed, a long periodof time for abrading is necessary. Further, an abrasive material of finegrade has a problem of loading. The term “loading” means that spacesbetween abrasive grains are filled with abrasion dusts that protrude toinhibit abrasive ability.

In case when an optical-fiber-connector end-surface is abraded by usingan abrasive material of which surface is flat, particles of abrasiondusts stay between abrasive grains, thereby abrasive grains become poorin cutting ability. The abrasive material described in the abovepublications has a flat abrasive surface, and cutting ability easilydecreases. Further, a liquid used as coolant or lubricant hardly worksbetween an abrasive material and an optical-fiber-connector end-surface,a part of the abrasive layer adheres to an abraded surface of theoptical-fiber-connector, and it is complicated in work for removing.

Japanese Patent Laid-open Publication No. 33372/1999 discloses anabrasive tape for an optical-fiber-connector end-surface which has anabrasive layer containing abrasive grains and a binder on a substrate,the abrasive grains being silica particles having an average particlesize of 5 to 30 nm, the abrasive layer being formed with cracks ofnetwork structure, so that abrasion dusts can be recovered on theabrasive tape.

Japanese Patent Laid-open Publication No. 2001-179640 discloses anabrasive material for an optical-fiber-connector end-surface which hasan abrasive layer containing abrasive grains and a binder on asubstrate, the abrasive layer having three-dimensional structureconstructed with a plurality of regularly arranged three-dimensionalelements having a predetermined shape. The abrasive layer of suchthree-dimensional structure easily let abrasion dusts out, and isresistant to loading and excellent in durability. Further, a smearhardly adheres on an abraded surface, and frequency in generation ofabrasion scratch is also very low.

However, in order to control generation of abrasion scratch moreeffectively, silica particles have to be used as abrasive grains,particle size have to be made small, and a binder contained in anabrasive layer have to be made soft. Although generation of abrasionscratch was effectively controlled in this case, it was newly discoveredthat adherent substance was generated on an abraded surface of opticalfiber with certain frequency.

If the adherent substance on an abraded surface of optical fiber is leftas it is, connection loss becomes large, whereas a cleaning step forremoving it, results in additional labor. Therefore, it is generallydesired a process for finish-abrading an optical-fiber-connectorend-surface without generating abrasion scratch on an abraded surface ofoptical fiber, nor generating adherent substance.

The present invention has been made to solve the aforesaid problems ofthe prior art and an object thereof is to provide a process forfinish-abrading an optical-fiber-connector end-surface withoutgenerating abrasion scratch on an abraded surface of optical fiber, norgenerating adherent substance.

SUMMARY

The present invention provides a process for finish-abrading anoptical-fiber-connector end-surface which comprises a step of abradingan optical-fiber-connector end-surface with using an abrasive filmcomposed of abrasive grains fixed on a film-form S substrate, in thepresence of a lubricating liquid, wherein the lubricating liquid is anaqueous solution containing a hydrophilic surfactant. The wording“hydrophilic” means that the surfactant has strong interaction withwater. Specific examples of the hydrophilic surfactant include ananionic surfactant such as RCOONa, RSO₃Na, and RSO₄Na, wherein Rrepresents a lipophilic group, a nonionic surfactant having a HLB valueof not less than 8, and the like.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a perspective view showing an embodiment of an abrasive filmused in a process of the present invention.

FIG. 2 is a microscope digital image showing an abraded surface withadherent substance of optical fiber.

FIG. 3 is a microscope digital image showing an abraded surface withoutadherent substance of optical fiber.

DETAILED DESCRIPTION

As described above, finish-abrading of an optical-fiber-connectorend-surface, is conducted by applying the optical-fiber-connectorend-surface to an abrasive surface of the abrasive film, and rubbingwhile applying a predetermined amount of pressure.

A non-limiting example of the abrasive film as used in thefinish-abrading step is abrasive films comprising a three-dimensionalstructure. Specific examples of such an abrasive film are described inWO92/13680, WO96/27189, Japanese Patent Laid-open Publication No.2001-179640, and the like. FIG. 1 is a perspective view showing anembodiment of the abrasive film preferred to be used in a process of thepresent invention.

The abrasive film 100 is an abrasive material which has a substrate 101and an abrasive layer 102 applied on a surface of the substrate. Theabrasive layer 102 contains matrix of a binder and abrasive grains 103dispersed therein.

The abrasive layer is formed by shaping and solidifying a slurrycontaining a plurality of abrasive grains dispersed in the binder whichis in an unhardened or ungelated state, i.e. the slurry is fixed to havea predetermined shape.

Size of the abrasive grains may vary depending on the type of theabrasive grains or the intended use of the abrasive material. Forexample, the grain size is 1 to 500 nm, preferably 5 to 200 nm for thefinish-abrading. Preferable material for the abrasive grains includessilica, aluminum oxide, and silicon carbide. Particularly preferable oneamong these is silica. This is because silica is the same in material asconventional optical fiber, and it hardly damages an abraded surface ofthe optical fiber.

The binder is hardened or gelated to form the abrasive layer. It ispreferred that the abrasive layer is formed so as to becomecomparatively soft in case of the finish-abrading. For example, Young'smodulus of the binder which forms matrix of the abrasive layer, isadjusted to 0.1 to 50 kg/mm², preferably 0.5 to 40 kg/mm². If theYoung's modulus of the binder is less than 0.1 kg/mm², abrasive grainshardly inroad the surface to be abraded, and cutting ability becomespoor. If it is more than 50 kg/mm², cushioning in contact between theabrasive grains fixed by the binder and the surface to be abradedbecomes poor, and abrasion scratch is easily generated on an abradedsurface of the optical fiber.

As the binder, variety of resins, for example, a thermocurable resin, athermoplastic resin, and a radiation curable resin may be employed.Preferred examples of the binder include an epoxy resin, and a urethaneresin.

The binder may be radiation curable. The radiation curable binder is abinder that is at least partially hardened or is at least partiallypolymerized by radiation energy. Depending on the binder to be used, anenergy source such as heat, infrared radiation, electron beam radiation,ultraviolet radiation, or visible light radiation is used.

Typically, these binders are polymerized by free radical mechanism.Preferred examples of the radiation curable binder are selected from thegroup consisting of acrylated urethane, acrylated epoxy, aminoplastderivative having an α,β-unsaturated carbonyl group, ethylenicunsaturated compound, isocyanurate derivative having at least oneacrylate group, isocyanate having at least one acrylate group, andmixture thereof.

The abrasive layer 102 has three-dimensional structure constructed witha plurality of regularly arranged three-dimensional elements 104 havinga predetermined shape. The three-dimensional elements 104 each have aprismatic shape formed of a laterally-placed triangular prism. Top angleβ of the three-dimensional element 104 is typically 30 to 150°,preferably 45 to 140°.

Ridges on the top of the three-dimensional elements 104 are located on aplane parallel to the surface of the substrate substantially over anentire region of the abrasive material. In FIG. 1, the symbol hrepresents height of the three-dimensional element from a surface of thesubstrate. The height h is typically 2 to 600 μm, preferably 4 to 300μm. Variation of height of the top lines is preferably less than 20%,more preferably less than 10%, of height of the three-dimensionalelement 104.

The three-dimensional element 104 preferably has two-layered structureincluding top portion 105 made of a layer containing abrasive grains anda binder, and foot portion 106 made of a binder. In FIG. 1, the symbol srepresents height of top portion of the three-dimensional element. Theheight s is, for example, 5 to 95%, preferably 10 to 90%, of the heighth of the three-dimensional element.

Typically, the three-dimensional elements 104 are arranged in a stripepattern. In FIG. 1, the symbol w represents length of short bottom sideof the three-dimensional element (width of the three-dimensionalelement). The symbol p represents distance between tops of adjacentthree-dimensional elements. The symbol u represents distance betweenlong bottom sides of adjacent three-dimensional elements. The length wis, for example, 2 to 2000 μm, preferably 4 to 1000 μm. The distance pis, for example, 2 to 4000 μm, preferably 4 to 2000 μm. The distance uis, for example, 0 to 2000 μm, preferably 0 to 1000 μm.

Length of the three-dimensional element may extend substantially over anentire region of the abrasive material. Alternatively, length of thethree-dimensional element may be cut to suitable length. Ends of thethree-dimensional elements may be either aligned or non-aligned. Theends of the prismatic three-dimensional elements may be cut at an acuteangle from its bottom to form house shape having four inclined surfacesin case that stronger cutting ability is required.

The abrading step may be conducted according to a conventional methodunder conventional conditions. For example, an abrasive machine in whichedge-abrasion is automatically conducted in case that anoptical-fiber-connector and an abrasive film are mounted, iscommercially available.

Water is conventionally employed as a lubricating liquid in conductingabrasion. This is because abrasion dusts are easily removed by waterflow, and a cooling effect is also obtained. In the present process, anaqueous solution containing a surfactant is employed as a lubricatingliquid instead of water, so that generation of adherent substance on anabraded surface of optical fiber is controlled.

A hydrophobic group of the surfactant is oriented to surfaces of theabrasive layer and the abrasion dusts, a hydrophilic group thereof isoriented to the contrary when a surfactant is added to the water to beused as a lubricating liquid, therefore a layer of the surfactant inmolecular order is formed. Due to layers made of the surfactant andwater, directly contacting area during abrasion between abrasive grainsand the surface to be abraded is reduced, dispersion of abrasion dustsinto the lubricating liquid is improved, re-adhering to the surface tobe abraded is controlled, and an abraded surface is kept clean.

As the surfactant, it is preferred that hydrophilic surfactants,particularly an anionic surfactant and a nonionic surfactant areemployed. Preferred nonionic surfactant includes those having a HLBvalue of 8 to 20, particularly 10 to 20. If the HLB value of thesurfactant is less than 8, the above described advantage is not obtainedbecause the lubricating liquid tends to form without emulsion.

Preferred examples of the anionic surfactant include alkylbenzenesulfonate. Specifically, sodium dodecylbenzene sulfonate is preferred.The preferred examples of the nonionic surfactant includepolyoxyalkylene nonyl phenyl ether, such as polyoxyethylene nonyl phenylether and oxyethylene oxypropylene block copolymer.

The surfactant is contained in the lubricating liquid in an amount of0.5 to 20% by weight, preferably 1.0 to 15% by weight, more preferably1.0 to 10% by weight. If the content of the surfactant is less than 0.5%by weight, the effect of controlling adherence becomes poor. If it ismore than 20% by weight, the lubricating liquid becomes viscous, andabrasion error may occur.

EXAMPLES

The present invention will be described in more detail by way of thefollowing examples. However, the present invention is not limited bythese examples.

An abrasive material coating liquid was prepared by mixing thecomponents shown in Table 1. TABLE 1 Dry Weight Non-volatile weightComponents (g) content (%) (g) Organosilica sol in isopropanol 100.00 30 30.00 (“IPA-ST” available from Nissan Kagaku K.K., average particlesize of 10 to 20 nm) Difunctional epoxyacrylate oligomer 4.20 100 4.20(“SP-1509” available from Showa Kohbunshi K.K.) Monofunctional acrylatemonomer 6.30 100 6.30 (“M-101A” available from Toa Gosei K.K.)Photopolymerization initiator 0.21 100 0.21 (“IRGACURE 907” availablefrom Ciba Specialty Chemicals K.K.) Total 110.71 40.71

A lamination binder was prepared by mixing the components shown in Table2. TABLE 2 Dry Weight Non-volatile Weight Components (g) content (%) (g)Monoacrylate monomer (“M-101A” 46.66 100 46.66 available from Toa GoseiK.K.) 75:25 mixture of difunctional 53.34 100 53.34 epoxyacrylateoligomer (“SP-1509” available from Showa Kohbunshi K.K.) andmonoacrylate monomer (“M-101A” available from Toa Gosei K.K.)Photopolymerization initiator 2.00 100 2.00 (“IRGACURE 907” availablefrom Ciba Specialty Chemicals K.K.) Total 102.00 102.00

A mold sheet made of polypropylene and having recesses with a shape ofinverted three-dimensional elements shown in FIG. 1 was prepared(“OFF-50” available from Minnesota Mining and Manufacturing Company).The abrasive material coating liquid was applied onto the mold sheet bymeans of a roll coater and dried at 50° for 5 minutes. The laminationbinder was applied thereon.

A transparent polyester film having a thickness of 75 μm (“HPE POLYESTERFILM” available from Teijin Dupon Film K.K.) was superposed and pressedby a roll for lamination. Ultraviolet rays were radiated to harden thelamination binder. The hardened binder had a Young's modulus of about 8kg/mm².

The mold sheet was removed and the resultant was cooled to roomtemperature to produce an abrasive film. The abrasive layer of theabrasive film has three-dimensional structure having a prismatic shapearranged in a stripe pattern as shown in FIG. 1. The dimensions thereofare shown in Table 3. TABLE 3 Symbol Size (μm) h 25 s 15 w 50 p 50 u  0β  90°

This abrasive film was stamped out into a circular shape having adiameter of 110 mm to prepare an abrasive disk.

An optical-fiber-connector end-surface was abraded with the use of theobtained abrasive disk. The abrasion conditions were shown in Table 4.TABLE 4 “OFL-12” available from Seiko Denshi Abrasive machine Kogyo Co.,Ltd. Load Point 1 (about 2 kg/cm²) Number of abraded samples 12Lubricating liquid Aqueous solution containing surfactant (Table 5)

The optical-fiber-connector, that is a sample to be abraded, waspreviously subjected to secondary-abrading by using “TRIZACT DIAMONDLAPPING FILM (3 mil, 0.5 micron)”, before conducting finish-abrading.After the finish-abrading is conducted, an abraded surface of theoptical fiber was observed by using a laser microscope, and checkedwhether the adherent substance was present or not. The results wereshown in Table 5. Yield as shown in Table 5 means a proportion (%) ofcount of samples without adherent substance to 12 samples simultaneouslyabraded. TABLE 5 Content Yield Surfactant HLB Run (%) (%) Pure water — 10 16.7 Sodium dodecylbenzene sulfonate — 2 1 100.0 (Anionic surfactant,“NEOPELEX F-25” 3 0.5 25.0 available from Kao K.K.) Polyoxyethylenenonyl phenyl ether 18.9 4 1 83.3 (Nonionic surfactant, “EMULGEN 985” 50.5 33.3 available from Kao K.K.) Oxyethylene oxypropylene block 16 6 10100.0 copolymer (Nonionic surfactant, 7 2 100.0 “PLURONIC F-68”available from Asahi 8 1 83.3 Denka Kogyo K.K., Mn = 8350, EO = 80%)Oxyethylene oxypropylene block 16 9 1 83.3 copolymer (Nonionicsurfactant, 10 0.5 41.7 “PLURONIC F-108” available from Asahi DenkaKogyo K.K., Mn = 15500, EO = 80%) Oxyethylene oxypropylene block 8 11 1025.0 copolymer (Nonionic surfactant, 12 2 16.7 “PLURONIC L-64” availablefrom Asahi Denka Kogyo K.K., Mn = 2900, EO = 40%)

FIG. 2 is a microscope photograph showing an abraded surface withadherent substance of the optical fiber (Run 1). FIG. 3 is a microscopephotograph showing an abraded surface without adherent substance of theoptical fiber (Run 7).

This results show that adherent substance was hardly generated on anabraded surface of optical fiber and yield for good article is improvedby adding a surfactant to a lubricating liquid.

According to a process for finish-abrading an optical-fiber-connectorend-surface of the present invention, no abrasion scratch is generatedon an abraded surface of optical fiber, nor adherent substance isgenerated.

1. A process for finish-abrading an optical-fiber-connector end-surfacewhich comprises a step of abrading an optical-fiber-connectorend-surface with using an abrasive film composed of abrasive grainsfixed on a film-form substrate, in the presence of a lubricating liquid,wherein the lubricating liquid is an aqueous solution containing ahydrophilic surfactant.
 2. The process according to claim 1, wherein theabrasive film comprises an abrasive layer which has abrasive grains anda binder, on a film-form substrate.
 3. The process according to claim 1,wherein the abrasive grains comprise silica having a grain size of 1 to500 nm.
 4. The process according to claim 2, wherein the binder has aYoung's modulus of 1 to 500 MPa.
 5. The process according to claim 2,wherein the abrasive layer has a three-dimensional structure constructedwith a plurality of regularly arranged three-dimensional elements havinga predetermined shape.
 6. The process according to claim 5, wherein topsof said three-dimensional elements are constructed with lines parallelto a surface of the substrate, and the lines are located on a planeparallel to the surface of the substrate.
 7. The process according toclaim 1, wherein the surfactant is an anionic surfactant.
 8. The processaccording to claim 1, wherein the surfactant is a nonionic surfactanthaving a HLB (hydrophilic lipophilic balance) value of 8 to
 20. 9. Theprocess according to claim 1, wherein the lubricating liquid has acontent of a surfactant of 0.5 to 10% by weight.
 10. The processaccording to claim 2, wherein the surfactant is an anionic surfactant.11. The process according to claim 3, wherein the surfactant is ananionic surfactant.
 12. The process according to 4, wherein thesurfactant is an anionic surfactant.
 13. The process according to claim5, wherein the surfactant is an anionic surfactant.
 14. The processaccording to claim 6, wherein the surfactant is an anionic surfactant.15. The process according to claim 2, wherein the surfactant is anonionic surfactant having a HLB (hydrophilic lipophilic balance) valueof 8 to
 20. 16. The process according to claim 3, wherein the surfactantis a nonionic surfactant having a HLB (hydrophilic lipophilic balance)value of 8 to
 20. 17. The process according to claim 4, wherein thesurfactant is a nonionic surfactant having a HLB (hydrophilic lipophilicbalance) value of 8 to
 20. 18. The process according to claim 5, whereinthe surfactant is a nonionic surfactant having a HLB (hydrophiliclipophilic balance) value of 8 to
 20. 19. The process according to claim6, wherein the surfactant is a nonionic surfactant having a HLB(hydrophilic lipophilic balance) value of 8 to 20.